Examination of high grade alloyed steels



fa IN ITED"'AS'TATES PATEN Patented July 9, 1935 T OFFICE v EXAMINATION OF HIGH GRADE ALLOYED i I Ekkehard Schauffele, Mannheim-Waldliof, V: 7

Germany No Drawing. ApplicationApril 2.5}1934, Serial No. 722,318. In Germany December 8, 1932 2 Claims.

My invention relates to the examination of metals and moreespecially high grade alloyed steels such as the so-called stainless steel with a view to ascertaining defective places. It is an object of my invention to provide means whereby the tracing of such defects is greatly simplified and facilitated. 1

As is well known to those skilled in the art, articles (including tools, vessels etc.) consisting 'of a high grade alloyed steel frequently possess a reduced resistivity against chemical and other influences in certain places, more especially at the welding scams or in places where they have-been subjected to changes of form in cold condition. For instance if during the welding operation certain precautionary measures are not sufiiciently observed, a change of the structure will arise at the welding seams, which may cause premature corrosion of the welded points, as distinguished from the material surrounding these places,

whereby the vesse1,tool or other apparatus may become altogether unfit for further use. It is therefore customary to examine the resistivity of such welding seams against corrosion according to certain methods enabling the operator to ascertain, before the apparatus or the like is put-to use, whether the condition of the welding seams involves danger'tc the apparatus as a whole. One of the methods particularly adapted for such examination and mostly in use is the so-called coption not only avoids these drawbacks, but it also altogether harmless, simple and applicable in the shortest possible time. It consists in the marking of the changes of structure by the production of colored compounds with the constituents of the alloy, which are exposed at the places, where the metal structure has undergone changes, but not in the unaffected steel. .The iron and nickel constituents of the alloy produce particularly good color reactions, since solutions of these metals can be traced easily and unambiguously for instance by means of compounds of complex iron compounds of the hydrocyanic acid such as potassium ferrocyanide or ferricyanide or by means of potassium thiocyanate and other thiocyanates or of dimethylglyoxime, etc.

In the practice of the new method the suspicious places are first treated with an acid and after removal of the acid by washing the color reagents are applied.

In accordance with a preferred form of my invention I apply these reagents under the form of a moist strip of paper or other tissue imbibed with the reagent in question or under the form of pastes or solutions capable of adhering to the places to be examined. I may for instance prepare such pastes or solutions by incorporating the color reagents in solutions, preferably aqueous or containing water, of gelatine, water glass glue or the like, or in a suspension of chalk having adhesive properties, or the like.

Obviously the kind, concentration and temperature of the acid and the period of time, during which it is allowed to act on the metal, must be so chosen that the acid will not attack the unaifected parts of the steel. As is well known, high grade steels are not attacked in the cold by dilute sulfuric or acetic acid or by nitric acid of any concentration. If anoxidizing acid such as nitric acid is used, if the test is made for free iron, 2. color reagent such as for instance potassium ferrocyanide must be used, which reacts with trivalent iron.

By proceeding in this manner all defective places of the material to be examined are rendered visible by a distinct color reaction, in contradistinction to the non-affected parts, which do not react with the reagent.

In practicing my invention I may for instance proceed as follows:

About grams potassium ferricyanide or a corresponding quantity of some other suitable color reagent are admixed under stirring to one litre of a hot highly viscous 20% solution of gela- I tine which at ordinary temperature has a jellylike consistency. The place of the alloyed steel to be examined is carefully freed from all impurities, which may for instance have remained over from the working tools. It is then exposed for about 10 minutes to the action of dilute sulfuric acid, for instance a 20% acid, whereupon it is freed from all but the last trace of the acid with I the aid of cleaning wool or cloth. The place is then covered by means of a brush free from iron with the testing preparation, which has preferably been slightly heated. The defective places will be copied in the preparation adhering to the metal under the form of a dark blue color precipitate.

The concentration of the sulfuric acid may be varied in accordance with the period of time, during which it is allowed to act on the metal.

Various changes may be made in the details disclosed in the foregoing specification without departing from the invention or sacrificing the advantages thereof.

I claim:-

1. The method of determining changes of internal structure or constitution in corrosion resistant alloy steels which may impair the strength and bring about corrosion of the metal, comprising treating a place to be tested with an acid which is inert with respect to the uninjured alloy, but capable of laying bare a constituent of the alloy in those places where the original structure of the alloy is defective, and thereafter applying a reagent capable of reacting with this constituent with the formation of a colored compound.

2. The method of determining changes of internal structure or constitution in welding seams of articles made from corrosion resistant alloy steels which may impair the strength and bring about corrosion of the metal, comprising treating such a welding seam to be tested with an acid which is inert with respect to the uninjured alloy,

but capable of laying bare a constituent of the 

